1. Field of the Invention
This invention relates generally to a solenoid with a selectively arrestible plunger movement, and more particularly, to a solenoid which may be energized in a select manner to arrest its plunger movement wherein the solenoid is particularly suitable for use with "scanning type" shutter blade elements so that means responsive to scene light can be utilized to energize the solenoid in the select manner to arrest the plunger and shutter blade movement thereby determining a maximum effective aperture size.
2. Description of the Prior Art
Automatic light responsive exposure control systems are well known in the photographic arts and have been long used to control the duration of photographic exposure intervals. Such systems may also be used in conjunction with an aperture defining mechanism so as to halt the mechanism at a position appropriate for operation under a desired exposure program prior to the actual exposure interval as is more fully described in a U.S. Pat. No. 3,641,891 entitled "Exposure Control System" by John Burgarella issued Feb. 15, 1972, and assigned in common herewith. The exposure control system of Burgarella provides for automatic sequential regulation, first of exposure aperture, and then of exposure interval. Voltage sensitive triggering circuits coupled to receive the output of a light sensitive circuit are used for controlling first the aperture mechanism, and then the shutter mechanism to provide a predetermined exposure program. Such an exposure control system may also be made sensitive to both ambient illumination and illumination derived artifically, thereby being useable in a "fill-in" flash function.
Exposure control systems have also incorporated what is termed a "follow-focus" system where the aperture adjusting mechanism is mechanically coupled with the focusing system of the camera. Thus, as the lens focus system is moved to provide the correct focus for a particular distance from the camera to the subject, the coupling mechanism of the follow-focus control system also moves to provide an appropriate exposure aperture opening in response to the focusing action thereby setting the exposure aperture in accordance with the anticipated light level at the scene to be photographed. Because of the known characteristics of the flashlamp being used, the anticipated light level at the scene to be photographed is functionally related to the distance to the subject. The automatic exposure control system which is responsive to both scene light by way of an exposure control circuit and to subject distance by way of a follow-focus setting is described in U.S. Pat. No. 3,464,332 issued to Davidson et al on Sept. 2, 1969. In the exposure control system of this patent, the aperture opening for admitting light to the film plane is automatically selected in accordance with the focusing of the camera and the exposure time is then controlled by a light detecting and integrating circuit so as to establish a unique interrelationship between the exposure aperture and exposure time.
Another exposure control system, as fully described in U.S. Pat. No. 3,522,763 entitled "Exposure Control Apparatus" by Milton Dietz, issued Aug. 4, 1970, and assigned in common herewith, automatically regulates the exposure interval when used in the flashmode of operation in accordance with either of two functions, the one being the level of illumination of the subject as photoelectrically sensed, and the other being the distance between the subject and the source of illumination. Thus the shutter automatically responds to both functions terminating exposure in accordance with one or the other, whichever is first to control the shutter. That portion of the exposure control circuit utilized to control the shutter as a function of the distance between the subject and the source of illumination embodies a timing circuit comprising a capacitor and variable resistor in cooperative association with the focusing means so that focus adjustment for subjects at a relatively great distance from the camera provides for a relatively high resistance, whereas focus adjustment for a subject relatively close to the camera position provides a relatively low resistance. Such a system is somewhat analogous to the above-described "follow-focus" system in that exposure interval is electronically controlled as a function of camera to subject distance, whereas in the "follow focus" system aperture size is mechanically controlled as a function of camera to subject distance. Not only may exposure interval be electronically controlled in the above-described manner by means of a variable resistor in cooperative association with the focusing means, but also exposure aperture may be automatically determined as a function of camera to subject distance by means of a variable resistor in cooperative association with focusing means as more fully described in U.S. Pat. No. 3,611,895 entitled "Photographic Camera For Use In Daylight and Artificial Light" issued Oct. 12, 1971. This patent discloses a photographic camera wherein the aperture size is determined both as a function of scene brightness and of the position of the focusing means when the exposure is made in artificial light.
All of the above-described exposure control systems, however, have one thing in common which is that they are designed for use with exposure apparatus having distinct mechanisms for determining exposure aperture and exposure interval, so that the aperture is determined prior to the actual commencement of the exposure interval. However, most recently, so-called "scanning type" shutter blade mechanisms have been found to be most advantageous. "Scanning type" shutter blade mechanisms generally embody two shutter blade elements formed with respective selectively shaped aperture openings therethrough which, depending upon the position of the blades, symmetrically overlap over a light entering exposure opening within the camera to define an effective scene light admitting aperture. Such blades, during an exposure interval, will move simultaneously and in correspondence with each other to define a symmetrically configured and progressively variable effective aperture opening over the camera light entering opening. Such "scanning type" shutter blade systems have been utilized in conjunction with automatic exposure control systems to automatically terminate exposure interval as well as with "follow focus" systems of the above-described type. Such shutter blade mechanisms have also included a driving solenoid which may be energized at a select current level to control the rate at which the shutter blade elements move thereby defining the rate of change of the effective scene light admitting aperture as is more fully described in a copending application for U.S. patent Ser. No. 350,025 by C. Peterson filed Apr. 11, 1973, in common assignment herewith. However, even these exposure control arrangements may not provide the requisite flexibility to achieve a particular exposure program. Increased exposure program flexibility may be provided by an automatic exposure control system utilized in conjunction with "scanning type" shutter blade elements wherein the maximum effective aperture to which the shutter blade elements progress during an exposure interval is controlled as an inverse function of scene brightness. Difficulty, however, arises in providing a solenoid suitable for first arresting the progress of the shutter blade elements to define the maximum effective aperture and thereafter driving the shutter blade elements to the closed position.
Therefore, it is also an object of this invention to provide a solenoid suitable for use in conjunction with "scanning type" shutter blade elements wherein the maximum effective aperture to which the shutter blade elements progress during an exposure interval is determined in accordance with a first select energization condition of the solenoid after which the shutter blade elements are returned to their closed position by the solenoid to terminate the exposure interval in accordance with a second select energization condition of the solenoid.
It is a further object of this invention to provide a solenoid for use in conjunction with "scanning type" shutter blade elements wherein the progressive movement of the shutter blade elements may be selectively arrested by the solenoid in accordance with a select energization condition of the solenoid.
It is an even further object of this invention to provide a solenoid for use in conjunction with "scanning type" shutter blade elements wherein the maximum effective aperture to which the shutter blade elements are allowed to progress by the solenoid is programmed inversely to scene brightness so that high levels of scene light intensity result in relatively small effective apertures while low levels of scene light intensity result in substantially smaller effective apertures.
Other objects of the invention will in part be obvious and will in part appear hereinafter.